Pilot's Handbook Of Aeronautical Knowledge Practice Test

Groundspeed is the speed at which the airplane moves over the Earth's surface. It’s the velocity relative to the ground, found by combining your airspeed with the wind. This differs from indicated airspeed, which is how fast you’re moving through the air itself. Wind can make groundspeed faster or slower: a tailwind increases it, a headwind decreases it, and a crosswind affects your track while still contributing to the resulting groundspeed. You use groundspeed to estimate time and distance en route, via time = distance / groundspeed. For example, 120 knots of airspeed with a 20-knot tailwind yields about 140 knots groundspeed; a 20-knot headwind yields about 100 knots. The other options refer to airspeed, a water-based context, or maximum indicated airspeed, not how fast you move over the ground.